Self-retaining diaphragm seal for recording instrument

ABSTRACT

A flexible diaphragm for a pressure recording instrument or the like which is provided with an annular groove around its periphery to define a resilient shoulder. The diaphragm is mounted in a coupling member which communicates with the instrument and is snapped into detachable securement over a projection or shoulder of the coupling member, which fits into the annular groove. The groove may carry an O-ring or similar compressible seal to effect a sealing engagement between the seat of the groove and the inserted shoulder, or the O-ring seal may be compressed against the coupling member by some peripheral portion of the diaphragm, such as a peripheral shoulder. Another sealing area may be provided by the abutment between the walls of the groove and the inserted shoulder of the coupling. Still another sealing area is provided by a marginal portion of the diaphragm which is compressed between the instrument coupling or flange member and another coupling or flange member is fastened thereto and which communicates with a process line.

limit ed Etates Patent Zavoda 1 lFeb. 29, 1972 [54] SELF-RETAININGDEAPHRAGM SEAL Primary ExaminerLouis R. Prince FOR RECORDING INSTRUMENT[72] Inventor: John R. Zavoda, 429 State Route 303, Streetsboro, Ohio44240 [22] Filed: .llune4,1970

[21] Appl.No.: 43,372

[52] U.S.Cl.... ...73/406,92/l02 [51] 1nt.Cl. ..G01l7/08 [58]FieldofSearch ..73/406,408;92/102, 104; 277/178 [56] References CitedUNITED STATES PATENTS 2,437,440 3/1948 Rigden ..73/406 UX 2,550,6725/1951 Chyba ..92/102 3,231,232 1/1966 Baumann... 92/102 X 1,108,1468/1914 Deegan 92/102X 1,964,745 7/1934 Sauzedde... ..92/ 102 3,209,72110/1965 Pall et a1. ..73/406 X Assistant Examiner-Daniel M. YasichAtt0rney1sler and Ornstein [5 7] ABSTRACT A flexible diaphragm for apressure recording instrument or the like which is provided with anannular groove around its periphery to define a resilient shoulder. Thediaphragm is mounted in a coupling member which communicates with theinstrument and is snapped into detachable securement over a projectionor shoulder of the coupling member, which fits into the annular groove.The groove may carry an O-ring or similar compressible seal to effect asealing engagement between the seat of the groove and the insertedshoulder, or the O-ring seal may be compressed against the couplingmember by some peripheral portion of the diaphragm, such as a peripheralshoulder. Another sealing area may be provided by the abutment betweenthe walls of the groove and the inserted shoulder of the coupling. Stillanother sealing area is provided by a marginal portion of the diaphragmwhich is compressed between the instrument coupling or flange member andanother coupling or flange member is fastened thereto and whichcommunicates with a process line.

4 Claims, 4 Drawing Figures PAIENTEDFEB29|912 3.645.139

INVENTOR. JOHN RZAVODA FKLZ WXW ATTORNEfS SELF-RETAINING DIAPHGM SEALFOR RECORDING INSTRUMENT BACKGROUND OF THE INVENTION In various processindustries, particularly the chemical process industries, variousliquids, gases or slurrys are maintained under vacuum or under pressure,either in vessels or in flow conduits, and the pressure values must bemonitored. For this purpose, suitable gauges or recording instrumentsare mounted on the process vessels or on the flow lines or are remotelycoupled thereto, to sense, indicate and record the existing pressurevalues.

In most chemical processes, as well as in many other process industries,it is both necessary and desirable to isolate the pressure sensing meansof the recording instrument from the abrasive or corrosive or gummingaction of the process material so that the sensing means will not besubjected to undue deterioration, injury or wear. To accomplish thisisolation, it is common practice to provide a flange member or similarcoupling unit having a cavity in communication with the pressurerecording instrument. This instrument flange member is secured inabutting relationship to a process flange member which has a cavity incommunication with the pressure fluid to be monitored. A flexiblediaphragm of metal, rubber or synthetic resin serves to partition theinstrument cavity from the process fluid cavity and is secured betweenthe coupling or flange members at its marginal portions. A suitablecompressible sealing gasket overlays the secured marginal portion of thediaphragm to effect the necessary seal on the margin of the diaphragmwhen the coupling members are bolted together or otherwise secured inoperational abutment.

One side of the flexible diaphragm is thereby exposed to the pressure ofthe process fluids. The cavity in the instrument flange on the otherside of the flexible diaphragm is filled with light oil or othersuitable hydraulic fluid for communication with the pressure sensingmeans. The central portion of the flexible diaphragm is displaced orexpanded in response to pressure fluctuations from the process fluidcavity and transmits these changing pressure values through thehydraulic fluid medium in the instrument flange cavity for sensing bythe recording gauge or instrument.

After some period of use, whose duration depends greatly upon thecharacter of the process fluid, the process fluid cavity as well as theprocess side of the flexible diaphragm will have gathered or accumulateda sufficient amount or quantity of deposits of sludge or precipitates orother solids from the process fluids to which it is exposed, so thatcleaning of the process cavity and the process flange becomes necessary.The frequency of this cleaning can be diminished by the use of variousforms of flush-out" arrangements and fittings in a manner known to theart, but eventually a more thorough cleaning becomes mandatory andrequires disassembly of the unit for access to the interior of theprocess flange member. Inasmuch as the marginal portion of the diaphragmis clamped between the two flange members, it no longer has anysecurement when the flange members are uncoupled for disassembly andcleaning. Its seal with the hydraulic instrument fluid is broken whenthe flanges are disassembled. This ordinarily results in the loss of allor a good part of this hydraulic fluid which must then be replaced whenthe unit is reassembled. The replacement of the hydraulic fluid is notonly a tedious and time-consuming task, but can also result in thenecessity for recalibrating the unit as a result of there being agreater or lesser quantity of the replacement hydraulic fluid than wascontained in the unit before the disassembly. The sealing gaskets willordinarily have acquired a permanent set which makes it necessary forthe gasket to be replaced after the cleaning operation has beencompleted and the unit is to be reassembled. If the gasket is notreplaced, it is quite likely that an imperfect seal between the couplingmembers will result on reassembly of the unit and that leakage willoccur.

In order to at least prevent the unnecessary loss of the hydraulic fluidfrom the instrument cavity, some of the prior art diaphragm sealsinclude a third coupling member or socalled middle ring" which issecured to the instrument flange member and serves to clamp thediaphragm in position, in lieu of using the process flange member forthis purpose. The process flange member is then secured to the middlering, independently of the securement of the middle ring to theinstrument flange member. By this arrangement, the process flange membercan be disassembled without disturbing the assembly of the diaphragm inits position between the instrument flange member and the middle ring.However, this arrangement represents a costly solution to the problem,as it requires an additional part in the fonn of the middle ring andthis additional part is exposed to the process fluid and must thereforebe made of the same type of material as the process flange, which isusually made of an extremely expensive noncorrosive nickle-bearing alloyor the like.

The foregoing disadvantages, as well as others to be described, areovercome by the self-retaining diaphragm of the invention.

SUMMARY OF THE INVENTION The invention relates to a self-retainingdiaphragm for a pressure recording instrument and the like which issnapped into securement in the cavity of the assembly, preferably in theinstrument flange member, so that when it is necessary to uncouple theflange members for cleaning or other attention, the diaphragm isretained by the instrument flange member in sealing engagement with thehydraulic fluid, without reliance upon any clamping securement betweenthe coupling members.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a view in elevation of apressure recording unit embodying the features of the invention.

FIG. 2 is an enlarged cross-sectional view, taken as indicated on line22 of FIG. I.

FIG. 3 is an enlarged fragmentary cross-sectional view of a portion ofFIG. 2 showing the peripheral sealing and securing means in greaterdetail.

FIG. 4 is a view similar to FIG. 3, but showing a modified form of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly toFIGS. 1-3 of the drawings, there is shown a conventional form ofpressure recording gauge or instrument 10 which is secured, as by theexternally threaded extension 11 to an instrument coupling or flangemember 12 in communication with a cavity 13 therein. The instrumentflange member 12 is secured in face-to-face abutment with a processflange member 14 which has a cavity 15 which is adapted to be connectedto a process flow line or receptacle through the internally threadedopening 16.

It will be understood that the term pressure" as used herein is intendedto broadly include subatmospheric pressures as well as greater thanatmospheric pressures. It will also be understood that although the unitis described as being mounted directly on a pipeline or process vessel,the principles of the invention can also be utilized in thoseapplications where the wnsing unit is more remote from the pressuresource.

A flexible diaphragm 17 of circular configuration is mounted on thecoupling flange 12 so as to provide a partition between the cavities 13and 15. As shown in FIG. 2 of the drawings, the diaphragm has a centralor body portion 18 of wavelike cross section to enhance the flexibilityand displacement characteristics of the diaphragm. Preferably, thediaphragm is molded as a single-unitary structure using Teflon or othersynthetic compositions having the necessary chemical and physicalcharacteristics which are desired for optimum performance of thediaphragm. However, the principles of the invention do not preclude theuse of metal or rubber or composite materials, such as a rubber bodywith a metal-reinforced periphery, for the structure of the diaphragm.

The body portion 18 of the diaphragm is surrounded by a peripheral ormarginal portion 19 of somewhat greater thickness than the body portion18, and which is provided with an annular groove 20 which lies orextends substantially in the plane of the diaphragm. The groove definesa resilient undercut shoulder 21 which extends outwardly from thediaphragm and is exposed to the instrument cavity 13. An underlyingshoulder or marginal portion 22 of the diaphragm is defined on theopposite side of the groove 20 and extends outwardly from the diaphragmand is exposed to the cavity 15.

The diaphragm 17 is secured in the instrument flange 12 by snapping itsmarginal portion 19 over and onto an annular inwardly directedprojection or shoulder 24 of the flange 12 which is received in theannular groove 20. The shoulder 21 extends outwardly from the base ofthe groove to overlie the shoulder 24 sufiiciently to restrain thedisplacement of the marginal portion of the diaphragm from itssecurement to the instrument flange member at the pressure operatingconditions to which it will be exposed. Ordinarily, the pressures on theopposite sides of the diaphragm are in equilibrium so that there is nosignificant differential pressure within the instrument cavity 13 whichwill tend to displace the marginal portion 19 from its snap-insecurement. For test purposes and to provide a margin of safety, theshoulder 21 may preferably be of a length sufficient to resistdisplacement of the marginal portion 19 when exposed to a differentialpressure of one atmosphere in the cavity 13. This is merely presented byway of example and is not to be construed as a limitation. The necessarylength of the shoulder 21 will also be affected by the strength,resiliency and physical characteristics of the material which is usedfor the diaphragm. These factors afi'ecting the dimension of theshoulder 21 to achieve the desired adequate securement, must in turn becompromised with the need for ease of assembly so that the installationof the diaphragm should not be unduly difficult and complicated. Theweighing and evaluation of such factors to properly dimension the lengthof the shoulder 21 is well within the skill of the art and requires nofurther elaboration.

Ordinarily, the opposite shoulder or marginal portion 22 will extendoutwardly from the diaphragm to a greater extent than the shoulder 21,as it is desirable that the portion 22 present a substantial surfacearea to the process cavity 15, as well as to the clamping surfaces ofthe coupling members 12 and 14 between which it is retained.

A compressible seal, such as an O-ring 23, is positioned in sealingengagement between the marginal portion 19 of the diaphragm and theinterior of the cavity 13. In the form of invention shown in FIGS. 2 and3 of the drawings, the seal 23 is shown as being positioned between thewall of the cavity 13 and the upper face 25 of the shoulder 21.

An annular groove 26 is provided below the projection 24 for receivingthe shoulder 22 of the diaphragm. The shoulder 22 is of slightly greaterthickness than the depth of the groove 26 in which it is received. Thelower surface 28 of the shoulder 22 thus extends beyond the lowersurface 29 of the coupling flange 12 and will be subject to some slightcompression between the upper surface 30 of the recess 26 and thesurface 31 of the process flange 14 when the flanges 12 and 14 aresecured in face-to-face relationship, as by the bolts 32 and nuts 33.

With the device assembled in the manner illustrated in FIGS. 1 and 2 ofthe drawings, and with the cavity 13 substantially filled with a lightoil or other suitable hydraulic medium, the O-ring 23 effects a sealagainst leakage of the instrument fluid from the cavity 13 regardless ofwhether the flange members 12 and 14 are clamped together or not.However, when the flange members are clamped together there is anadditional axial thrust or force transferred to and imposed upon theO-ring 23 which further augments the sealing force imposed upon theO-ring by its engagement with the surface 25 of the shoulder 21.

In addition to the primary seal effected by the O-ring 23, a secondaryseal is effected between the upper surface 30 of the recess 26 and theupper surface 27 of the shoulder 22. This secondary seal is, to someextent independent of the coupling of the flange member 14 to the flangemember 12, although it is of course augmented and perfected as a resultof the clamping action of the bolts 32 upon the shoulder 22. The sealingengagement between the surfaces 27 and 30 would at least preventtainting of the process fluid by the instrument fluid as long as theflange members 12 and 14 are in the clamped relationship, even thoughthe primary seal 23 should become ineffective for some reason. Althoughthe possibility of the seal 23 becoming ineffective is quite remote, theutilization of a secondary sealing area is advisable, particularly whenthe process fluid relates to foods or drugs.

In addition to the secondary seal provided between the surfaces 27 and30, there is another secondary seal which may be provided between thesurfaces of the projection 24 and the walls of the diaphragm groove 20.These parts may be so dimensioned that the projection 24 will bereceived snugly in the groove 20 and will create a secondary sealagainst leakage of fluid from the instrument cavity 13 regardless ofwhether the flange members 12 and 14 are in coupled relationship or not.

The body portion 18 of the diaphragm 17 will be displaced by thepressure differential between the respective cavities 13 and 15 so as toreflect the process pressures to the pressure recording instrument 10.It will be noted that as the body portion 18 of the diaphragm isdisplaced upwardly in the cavity 13, there is an increased axiallydirected component of force on the O-ring 23 which further augments thesealing action of that O-ring. Conversely, the O-ring resists and tosome slight degree restricts this displacement of the diaphragm bodyportion 18, thus resulting in some slight loss of sensitivity of thediaphragm in the pressure sensing function. This slight loss ofsensitivity is not critical or significant in many pressure sensingoperations, but may be of significance in some others. Additionally,when the monitored process is an uninterrupted one intended to run at afairly uniform pressure for long periods of time, it is possible thatthe O-ring 23 will attain a permanent set resulting from the augmentedaxial component of force previously described, so that when the flangemembers 12 and 14 are uncoupled, the desired zero leakage of the seal 23will not be achieved. As is known to the art, the problem of hysterisisor delayed recovery of the seal 23 in response to relieved compressiveforce, must also be considered as a factor in designing a seal whichwill achieve zero leakage. These problems are effectively overcome bymounting the O-ring in the groove 20 as illustrated in FIG. 4 of thedrawings.

In the modified form of invention shown in FIG. 4, an O- ring 34, whichmay be of considerably smaller cross section than the O-ring 23, ismounted in the base of the groove 20in sealing engagement with the end35 of the projection 24. The sealing force on the O-ring 34 issubstantially in the direction of the plane of the diaphragm 17 and isdiametrieal rather than axial, as in FIG. 3. The operative displacementor flexing of the body portion 18 of the diaphragm has no significantcompressive effect upon the O-ring 34 so that the hysterisis ornonrecovery problem is minimized in those process applications where itmight exist and be a troublesome factor. In contrast to the form ofinvention shown in FIG. 3, the O-ring 34 does not resist or restrict theflexing movement of the body portion 18 of the diaphragm so that thereis no damping of its sensitivity, as was possible by the O-ring 23.Thus, by mounting the O- ring in the groove 20 the problems of permanentset and of hysterisis and of interference with sensitivity are overcome.The arrangement of FIG. 4 is therefore preferred over that of FIG. 3,particularly in the applications where a high degree of sensitivity ofpressure recording is sought. There may be unusual circumstances whereit may be desirable to utilize the seals 23 and 34 in combination andthis is contemplated as being within the scope of the invention.

It will be noted that in both forms of the invention, the effect of anincrease in pressure in the cavities 13 and 15 will be translated intoaugmented sealing engagement as a result of either cold flow at themargin of the diaphragm or greater compressive force on the sealingsurfaces or a combination of both these factors. For this reason, thedevice can be effectively and successfully utilized for extremelyhigh-pressure sensing conditions, where devices of this type haveheretofore not been effective.

Regardless of which arrangement is used, the arrangement of MG. 3 or thearrangement of FIG. 4 or a combination of these arrangements, the unitmay be disassembled for cleaning without disturbing the primary sealseffected by the O-rings 23 and 34 and without losing any of thehydraulic fluid from the cavity 13. When the securing or clampingelements 32-33 are removed, the instrument flange 12 can be withdrawnbodily from its abutment with the process flange 14 without disturbingthe assembly of the diaphragm 17 with the instrument flange. Thisresults from the fact that the diaphragm 17 is selfretaining on theinstrument flange and does not rely upon the clamping action between theabutting surfaces of the flanges l2 and 14 for retention or for itsprimary sealing engagement with respect to the cavity 13. The problem ofreplacing a gasket has been completely eliminated by the self-retainingdiaphragm, and the task of refilling the cavity 13 with the hydraulicfluid has also been eliminated, thus eliminating the necessity forrecalibration of the unit after it has been reassembled. This has beenaccomplished without introducing the costliness and leakagevulnerability of an additional coupling member such as the middle ringpreviously mentioned. In addition to providing the self-retainingdiaphragm, the invention also provides an improved seal arrangement forthe instrument cavity with secondary seals to assure effectivefunctioning if there is any failure of the primary seal.

Although the device has been described as having a shoulder 22 receivedin the annular groove 26 of the instrument flange 12, it will beapparent that the clearance space provided by the annular groove 26could with equal facility be provided in the abutting surface of theprocess flange 14 or could be provided by complementary annular groovesin both of the flange members.

lclaim:

l. In a diaphragm assembly for a recording instrument, the combinationof a coupling member having a cavity in communication with theinstrument, an annular projection of said coupling member extendinginwardly into said cavity, a selfretaining pressure-responsive diaphragmhaving a peripheral annular groove in the general plane thereof anddefining an undercut yieldable shoulder element, said projection beingreceivable in said groove by deformation of said yieldable shoulderelement for releasably securing said diaphragm in said cavity, and acompressible seal for said cavity carried in said diaphragm groove andengaging said projection on said coupling member.

2. A combination as defined in claim 1, wherein said yieldable shoulderelement impresses a compressive force on said compressible seal in thedirection of the general plane of said diaphragm.

3. A combination as defined in claim 1, wherein said projection is insealing engagement with the walls of said groove to effect a secondaryseal for said cavity.

4. A combination as defined in claim 1, including a second couplingmember secured in face-to-face relationship with said first-namedcoupling member and defining a second cavity on that side of saiddiaphragm opposite to said first-named cavity, and a second compressibleseal comprising a marginal portion of said diaphragm disposed incompressible relationship between said coupling members.

1. In a diaphragm assembly for a recording instrument, the combinationof a coupling member having a cavity in communication with theinstrument, an annular projection of said coupling member extendinginwardly into said cavity, a self-retaining pressure-responsivediaphragm having a peripheral annular groove in the general planethereof and defining an undercut yieldable shoulder element, saidprojection being receivable in said groove by deformation of saidyieldable shoulder element for releasably securing said diaphragm insaid cavity, and a compressible seal for said cavity carried in saiddiaphragm groove and engaging said projection on said coupling member.2. A combination as defined in claim 1, wherein said yieldable shoulderelement impresses a compressive force on said compressible seal in thedirection of the general plane of said diaphragm.
 3. A combination asdefined in claim 1, wherein said projection is in sealing engagementwith the walls of said groove to effect a secondary seal for saidcavity.
 4. A combination as defined in claim 1, including a secondcoupling member secured in face-to-face relationship with saidfirst-named coupling member and defining a second cavity on that side ofsaid diaphragm opposite to said first-named cavity, and a secondcompressible seal comprising a marginal portion of said diaphragmdisposed in compressible relationship between said coupling members.